package duxiaomang;

import java.util.Arrays;
import java.util.Scanner;

/**
 * @author xizizzz
 * @description: TODO
 * @date 2021-9-5下午 03:26
 */
public class Test1 {
    public static void main(String[] args) {
        final Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int k = scanner.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) {
            arr[i] = scanner.nextInt();
        }
        int fenmu = 0;
        for (int i = 1; i < n; i++) {
            fenmu += i;
        }
        int res = 0;
        Arrays.sort(arr);
        for (int i = 0; i < n; i++) {
            for (int j = i + 1; j < n; j++) {
                if ((arr[j] - arr[i]) <= k) {
                    res++;
                }
            }
        }
        if (res == 0 || n == 0) {
            System.out.println("0/1");
            return;
        }
        if (res == fenmu) {
            System.out.println("1/1");
        } else {
            int temp = gcd(res, fenmu);
            System.out.println(res / temp + "/" + fenmu / temp);
        }
    }

    //辗转相除法求最大公约数
    static int gcd(int a, int b) {
        if (a % b == 0) return b;
        else return gcd(b, a % b);
    }

}
